Automotive air induction systems typically include an intake manifold having runners leading to the engine cylinders. As shown in FIG. 10, throttle body 30, which contains a throttle valve (not shown) for controlling the flow of air into intake manifold 10, is attached to manifold inlet 18. Traditionally, threaded fasteners are used to mount throttle body 30 to manifold inlet 18, with a flat gasket (not shown) placed therebetween to obtain a proper seal. For example, bolts 82 screwed through connecting plate 80 attach throttle body 30 to manifold 18 (FIG. 10).
A problem arises because stress relaxation of the sealing surfaces may render it difficult to maintain a sufficient sealing load on the gasket when the joints described above are used with plastic composite assemblies. Stress relaxation results when the load applied to ensure proper sealing causes the plastic composite material to deform. As use of plastic composites for the manifold and throttle body becomes increasingly common, new ways of ensuring a proper seal have become necessary. One such way is to provide receptacles in the intake manifold having metal fittings for receiving bolts. Problems with this type of joint, however, are that it can be difficult to assemble and expensive to manufacture.